1. Field of the Invention
The present invention relates to a fixing apparatus that is used in an electrophotographic apparatus, an electrostatic recording apparatus and the like and, more specifically, to a fixing apparatus in which a temperature detecting element is arranged on a heating element in a non-contact state.
2. Description of Related Art
Many fixing apparatuses such as a fixing apparatus of a roller system using a heating roller that is heated by a halogen heater and a fixing apparatus of a belt system for heating a heat-resistant belt by a ceramic heater or a halogen heater are used in image forming apparatuses such as a copying machine and a laser printer.
In such fixing apparatuses, temperature detecting means such as a thermistor for maintaining a surface temperature of a heating roller at a predetermined temperature and a temperature fuse or a thermoswitch for breaking a power supply path to a heater when a temperature of a heating roller rises to an abnormal level is often caused to abut a surface of a fixing roller or a fixing belt that contacts a recording material.
As a result, a contact damage occurs on the surface of the fixing roller or the fixing belt, which may cause a problem such as a white streak, a black streak and defective fixing.
Thus, it is possible to employ a method of causing the temperature detecting means to abut the surface of the fixing roller or the fixing belt outside an image area where the recording material passes. However, since detection of a temperature in the image area is impossible and the fixing apparatus becomes larger in size, a method of bringing the temperature detecting means close to the fixing roller within the image area in a non-contact state has been considered recently.
As the temperature detecting means for detecting a temperature of the fixing roller in a non-contact state, for example, there are temperature detecting means that uses a thermopile or arranges a thermistor on an infrared ray absorbing film functioning as a film member. The non-contact temperature detecting means is provided with a casing having an opening portion, an infrared ray absorbing film that is contained in this casing and consists of a polymeric material for absorbing an infrared ray that has passed through the opening portion, a thermistor element for film temperature detection that is disposed in close adherence to this infrared ray absorbing film, and a thermistor element for temperature compensation for detecting an ambient temperature in the vicinity of this thermistor element for film temperature detection.
Here, the non-contact temperature detecting means will be described.
In this non-contact temperature detecting means, an infrared ray that has passed the opening portion of the casing is absorbed by the infrared ray absorbing film disposed immediately below the opening portion, whereby the temperature of the infrared ray absorbing film rises. Then, the thermistor element for film temperature detection, which is disposed in close adherence to the infrared ray absorbing film, detects the change in temperature. The thermistor element for temperature compensation for measuring an atmospheric temperature in the casing is disposed in the vicinity of the thermistor element for film temperature detection. A difference between temperatures detected by the thermistor element for film temperature detection and the thermistor element for temperature compensation, respectively, is detected as a potential difference by a bridge circuit, whereby an absolute amount of the infrared ray that has passed the opening portion is detected and a temperature of the measured member is measured in a non-contact state. In this way, in the non-contact temperature detecting means, a temperature of the fixing roller or the fixing belt can be detected by measuring the temperature of the film that has absorbed the infrared ray.
With such non-contact temperature detecting means, a temperature of a fixing roller is estimated and detected by receiving or absorbing an infrared ray emitted from the fixing roller, which is an object of temperature detection. Thus, a temperature detecting ability of the temperature detecting means can be improved by increasing an infrared ray emissivity of the fixing roller. Therefore, a method of increasing the infrared ray emissivity by mixing carbon black in a material forming a surface layer of the fixing roller has been considered.
However, with the above-described conventional temperature detecting means, since a change in the temperature of the fixing roller is estimated and detected by receiving or absorbing an infrared ray emitted from the fixing roller, which is an object of temperature detection, if the fixing roller is contaminated by toner while being used or toner is offset on the fixing roller, a detected temperature deviates.
As a result, if the temperature detecting means detects a temperature on the surface of the fixing roller as a temperature higher than an actual temperature, a controlled temperature of the fixing roller drops lower than a predetermined value. However, a harmful effect in this case is defective fixing or jam due to defective separation, which means that a recording material cannot be separated from the fixing roller. An image forming apparatus suffered from such a harmful effect can be restored by cleaning the surface of the fixing roller or replacing the fixing roller. On the other hand, if the temperature detecting means detects a temperature on the surface of the fixing roller as a temperature lower than an actual temperature, a controlled temperature of the fixing roller exceeds the predetermined value. Then, since a temperature inside an image forming apparatus rises abnormally by heat from the fixing apparatus, a lot of harmful effects occur. For example, toner in a developing device of the image forming apparatus becomes solid, a security problem arises due to the abnormal temperature rising, an excessive temperature rising detecting member provided in addition to the temperature detecting means detects excessive temperature rising of the fixing roller, and a rubber material and the like used in the fixing roller of the fixing apparatus deteriorates earlier. It requires a lot of time and costs to restore the image forming apparatus.
Thus, it is an object of the present invention to provide a fixing apparatus that can detect a temperature of a fixing member without detecting it as a temperature lower than an actual temperature, even if the fixing member is contaminated by a developer and can prevent a lot of harmful effects as described above and an image forming apparatus provided with this fixing apparatus.
On the other hand, with the non-contact temperature detecting means, since a temperature of the fixing roller or the fixing belt is detected by measuring a temperature of the film that has absorbed an infrared ray, a difference of resistance values of the thermistor element for temperature compensation and the thermistor element for infrared ray detection can be increased at the time when a certain amount of infrared ray is absorbed in the infrared ray absorbing film by increasing an infrared ray absorptivity of the infrared ray absorbing film, and the temperature detecting ability of the temperature detecting means can be improved. Therefore, a method of mixing carbon black in the infrared ray absorbing film or coating the surface of the infrared ray absorbing film with a blackbody paint has been considered.
However, with the above-described non-contact temperature detecting means, a change in a temperature of the infrared ray absorbing film that has absorbed an infrared ray emitted from a fixing roller or a fixing belt, which is an object of temperature detection, is detected. Therefore, if the infrared ray absorbing film is contaminated by toner scattered in the fixing apparatus, wax contained in the toner or silicon oil or the like applied to the fixing roller or the like as a release agent, a detected temperature deviates. As a result, if the temperature detecting means detect a temperature on the surface of the fixing roller as a temperature lower than an actual temperature, abnormal temperature rising of the fixing roller occurs, which causes a security problem or results in earlier deterioration of the fixing roller and the like of the fixing apparatus.
Therefore, in order to prevent deterioration and the like due to abnormal temperature rising of the fixing roller, there is required a method which does not detect a temperature on the surface of the fixing roller as a temperature lower than an actual temperature, even if the infrared ray absorbing film is contaminated by toner or the like.
The present invention has been devised in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a heating apparatus that can detect a temperature of a fixing member without detecting it as a temperature lower than an actual temperature, even if the fixing member is contaminated by a developer, or even if a film of infrared ray detecting means is contaminated by a developer or the like, thereby preventing deterioration and the like of a fixing apparatus and an image forming apparatus due to abnormal temperature rising of the fixing member.
It is another object of the present invention to provide a fixing apparatus including: a fixing member which is heated by a heating member, for heating and fixing a toner image on a recording material; temperature detecting means for detecting a temperature of the fixing member by absorbing an infrared ray emitted from the fixing member; and controlling means for controlling power-supply to the heating member, based on an output of the temperature detecting means, in which an infrared ray emissivity of the fixing member is lower than an infrared ray emissivity of the toner within a detection range of the temperature detecting means.
It is still another object of the present invention to provide a fixing apparatus including: a fixing member which is heated by a heating member, for heating and fixing a toner image on a recording material; a film for absorbing an infrared ray emitted from the fixing member; temperature detecting means for detecting a temperature of the film; and controlling means for controlling power-supply to the heating member, based on an output of the temperature detecting means, in which an infrared ray absorptivity of the film is equal to or lower than an infrared ray absorptivity of the toner within a wavelength region emitted from the fixing member.
It is still another object of the present invention to provide a fixing apparatus including: a fixing member which is heated by a heating member, for heating and fixing a toner image on a recording material; an oil for being applied onto the fixing member; a film for absorbing an infrared ray emitted from the fixing member; temperature detecting means for detecting a temperature of the film; and controlling means for controlling power-supply to the heating member, based on an output of the temperature detecting means, in which an infrared ray absorptivity of the film is equal to or lower than an infrared ray absorptivity of the oil within a wavelength region emitted from the fixing member.
It is still another object of the present invention to provide a fixing apparatus including: toner which contains wax; a fixing member which is heated by a heating member, for heating and fixing a toner image on a recording material; a film for absorbing an infrared ray emitted from the fixing member; temperature detecting means for detecting a temperature of the film; and controlling means for controlling power-supply to the heating member, based on an output of the temperature detecting means, in which an infrared ray absorptivity of the film is equal to or lower than an infrared ray absorptivity of the wax within a wavelength region emitted from the fixing member.
Still other objects of the present invention will be apparent in the following description.